Disposable-filter holders in question as a rule comprise a plastic, two-piece housing of which the housing halves are connected to each either in pressure-resistant manner; they are flat and boxy. Inside such filter holders there is an essentially flat cavity divided by a filter, ordinarily a membrane filter, into an intake side pressure chamber and a discharge-side filtrate chamber. Typically the filter is secured against tearing by a filter support, for instance in the shape of a disk.
Single-use, i.e. disposable filter holders of this species are used wherever it is desired to filter preferably small and minute fluid volumes rapidly, reliably and in sterile manner as called for. As regards general lab work, there are many applications, illustratively preparing high-purity solutions of reaction. Another substantial application is medical and pharmacological lab work.
The plurality of these applications requires filter holders which for equal external dimensions of housing and filter merely differ relative to the filter characteristics, for instance the filter material or its pore size and sterility. The disposable filter holder in question being mass produced, there is a mandatory need for reliable, simple and differentiable characterization of the product. This differentiation illustratively can be carried out by individually characterizing either or both housing pieces, for instance by coloring the housing material or by applying a characterizing imprint. Disposable-filter holders so characterized however incur the drawback that if a change in type production takes place, either the mold must be changed or the entire injection machine, including the extruder, must be cleaned. Moreover vast storage of differently characterized housing pieces is required. Such steps significantly make such disposable-filter holders more expensive.
A solution to this problem is known from the German patent document No. 28 37 058 C3 in that disposable-filter holders of different types are manufactured with the same housing. The housing halves in this solution are identical for all given types and are joined--with inserted membrane filter--in geometrically locking or non-positive manner and then are sealed by injection molding in an appropriate sealing mold using a plastic sealing ring dyed to correspond to the filter characteristics and so as to be gas-tight and pressure-resistant.
However this known disposable-filter holder incurs the drawback that the dyed ring simultaneously acts to seal and lock on one hand and on the other to mark. This requires that this sealing ring on one hand be designed to engage around both the upper and lower pieces of the housing, while on the other hand it must be fairly thick. Accordingly the preparation of the sealing ring requires a comparatively large quantity of the dyed plastic of which the introduction into the mold furthermore often entails laborious or expensive design steps. Again the peripheral sealing ring enlarges rather significantly the outside diameter of the filter which as a rule is between one and five cm, and thereby the manufacturer once more incurs additional packing and storage costs which are always critical with mass produced items.
In the light of that state of the art, it is the object of the present invention to create a disposable, i.e. single-use filter holder of the initially cited kind which can be manufactured economically and for which the sealing and locking functions on one hand and the characterization on the other are separate and which makes possible reliable, permanent color-coding of the disposable-filter holder without the deposition of the color code means entailing an increase in the outside dimensions of the disposable-filter holder.